With the advance of the technology, mobile electronic devices have become indispensable products for most people. As mobile electronic devices become more and more compact than before, various antennas with different sizes and functions are developed in order to conform to the requirements of various mobile electronic devices (e.g. mobile phone, notebook, etc.) and wireless transmission devices (e.g. wireless access point, wireless network card, etc.). Several kinds of antennas have been comprehensively applied to mobile electronic devices, such as the planar inverse-F antenna (PIFA), the monopole antenna or the dipole antenna because these antennas have compact size, good transmission performance and can be easily installed on the inner wall of a mobile electronic device.
However, the conventional dipole antennas still have a lot of shortcomings to be overcome. For example, as the width of most conventional dipole antennas is wide in comparison, it may take up too many space available in an antenna structure, and thus the conventional dipole antennas may not be suitable to be used in the modern electronic devices that are becoming smaller and smaller.
Therefore, it has been an important issue to provide a dipole antenna with a width to be formed as narrow as possible.